I am a closet GURPs fan. While I did some work/ playtest for Hero some years back, my first regular campaign was The Fantasy Trip, aka GURPS V0.2. I have a soft spot for the game that is the descendent of my first game. The source materials alone have made being fluent with the game system worth it.
As for 4th edition:
It is a nice five star set of book.
Color Coded section.
Lots of Example
Use of color on the pages to highlight things.
Cost! 70 Bucks for the two main books...
Attributes costs have been simplified.
Attribute cost for STR & Health is now 10 pts level, the more useful DEX & IQ are 20 pts a level.
Advantages and Disadvantages have been condense into one book and better defined. They are also coded as physical/ mental/ social with the modifiers of paranormal/ supernatural/ mundane. None of the "odd" or "environment specific" advantages and disads are included, but they have included all the generally usable ones in the book. Note some of the advantages/ disadvantages are from Supers/ Aliens, and usable for making races and some supers.
The Skills list in inclusive as well, with all the odd specialties added in. No more searching through six books and the almanac. The new skills rules and costs have been clarified in short sections. Specialties and defaluts are well thought out and simplified.
Same advanages, color coded, clear and concise descriptions.
The combat system has been quite cleaned up. Even though it is still one second turns, the rules now make more sense.
There are tactical and environment rules for a variety of situation, vehicle rules, animal creation, template creation, and a many things a GM needs.
There is a section on World Design/ Campaign Design which is not that impressive.
It includes the time line world (Centrum and Timeco) from Time Travel, now Alternate History 1.
While the game is still a tool kit, there is still need for genre specific setting books. (i.e. while there are guidelines in this book, they are not as useful for creating new things as they could be.) It is a good solid game. They really got it right this time. Now lets see what they do with it.
It is not a D20 killer by any stretch of the imagination, but it will give you an option.